There is one pattern I tie for a friend that has green dyed teal as a collar at the head. The teal being spun onto the hook shank right at the start of tying then folded back like the blue jay is in Irish Bumbles. He uses it on Badanloch, I've tried it on other lochs but never caught on it.
I have also seen it used in Irish Dabbler style flies in place of the mallard for the veiling. Though this is more a winging technique than a hackling one, though the finished effect is more like a spey hackle than a wing.
The difficulty in tying a hackle in proportion to a trout fly is, I think, what has stopped it from being used in this way.
"Political correctness is a doctrine, fostered by a delusional, illogical
minority, and rabidly promoted by an unscrupulous mainstream media, which
holds forth the proposition that it is entirely possible to pick up a ****
by the clean end"